1. Field of the Invention
The present invention relates to a cut-web tail edge holding means for web winding apparatus.
2. Description of the Prior Art
Conventional web rewinders for rewinding webs of sheet material, such as paper, from big rolls into smaller rolls includes a web separating (cutting) device for cutting a continuous web to a desired length, of the type as described in, for example, U.S. Pat. Nos. 3,552,670 and 4,487,377.
Such known web winding apparatus, as FIGS. 8 and 9 show (which drawings are based on like drawings given in U.S. Pat. No. 4,487,377), has a main winding drum 35 and a web separator roll 40 which are operatively interconnected so as for them to rotate in synchronism, the main winding drum 35 having a channel 42 in the surface thereof, the web separator roll 40 having a web separator device 41 projecting from the surface thereof, the channel 42 and the web separator device 41 being so formed in the main winding drum 35 and the web separator roll 40 respectively that at selected times during synchronous rotation of the main winding drum 35 and the web separator roll 40 the web separator device 41 is forced into the channel 42, the web separator device 41 having a rigid member 43 which forces the web 31 into the channel 42 such that when the rigid member 43 is forced into the channel 42, the web separator device 41 will move the web 31 into the channel 42 a distance in excess of the stretch and tensile characteristics of the web so as to tear the web in the channel 42.
In web rewinders having such a web separator device, once a continuous web is severed (cut), it is impracticable to move the leading edge 31a of the severed web 31 to a position at which the leading edge 31a is to be put in contact with a core 38 for a next roll of web, because the leading edge 31a and trailing or tail edge 31b of the severed web 31 are already separated from the surface of the drum 35 against which they had been integrally held; it is also impracticable to keep the tail edge 31b of the severed web 31 from coming in contact with the surface of the core 38 which is usually coated with an adhesive.
In order to avoid such inconvenience, therefore, it is usual practice with apparatus of the above mentioned type that the main winding drum 35 is equipped with a vacuum arrangement so that even after web 31 severance has taken place, both the leading edge 31a and the tail edge 31b of the web are held against the main winding drum 35 at locations adjacent the channel 42 and over a certain distance of rotation.
The main winding drum 35 is formed in its surface with suction ports 46, 50 which are arranged at opposite sides of the channel 42 and in circumferentially spaced apart relation therewith. According to this arrangement, the leading edge 31a and tail edge 31b of the severed web can be held in suction by these suction ports 46, 50, whereby they may be held against the surface of the main winding drum 35 over a specified distance of drum rotation. The tail edge 31b of the severed web may be held in abutment against the surface of the main winding drum 35 so as for it not come in contact with the adhesive coated surface of the core 38.
In the prior art apparatus, in order to enable the tail edge 31b of the severed web to be held in contact with the surface of the main winding drum 35 until it passes a predetermined position and also enable the leading edge 31a of the severed web to be held against the surface of the main winding drum 35 until it reaches a predetermined position, and then to enable both the leading and tail edges 31a, 31b to be disengaged from the drum surface, as FIGS. 8 and 9 show, the interior of the main winding drum 35 is defined into two chambers, namely, a vacuum chamber 53 and an atmospheric chamber 54 by two partition walls 51, 52, the vacuum chamber 53 being constantly in communication with a vacuum source, the atmospheric chamber 54 being not connected to the vacuum source. Means are provided at the partition walls 51, 52 for starting and stopping vacuum action for web suction by the suction ports 46, 50. Such arrangement involves considerable elaborateness in construction. In particular, spacious interior of the main winding drum 35, a rotating body, must be defined into two chambers by partition walls 51, 52, non-rotating stationary members, which must be firmly fixed in position so as not to rotate and airtightly held at their ends in sliding contact with the inner periphery of the main winding drum 35.
This drawback may be overcome by, for example, arranging that in the interior of the main winding drum 35 a vacuum chamber is defined by a partition wall rigidly fixed to the inner surface of the drum 35, with suction ports 46, 50 so formed as to open into the vacuum chamber, and that the vacuum chamber is adapted to be connected through a valve plate (like a timing plate for an axial piston diagonal plate type hydraulic motor), mounted to a side of the main winding drum 35, to the vacuum source only for a limited part of one rotation (not shown). In this case, however, there must be two vacuum chambers which are rotatable integrally with the main winding drum 35, or otherwise it is impracticable to arrange that two suction ports 46, 50 located at different phases of rotation can effectively be released at a specified phase of rotation of the drum 35 from the vacuum source.
Furthermore, such vacuum arrangement involves other problems, such as high power consumption and high noise due to vacuum air (which makes a source of noise). Another problem is that the suction port 50 with which the tail edge 31b of the severed web comes in contact is liable to dust deposition, which requires frequent cleaning.